Leeks started indoors

If they've literally just come through they should be OK put straight outdoors under cover (GH or cold frame for example.)

If they've already straightened up it probably would be wise to bring them back inside for a few nights if they are very cold because the leaves could already be a little 'soft'.

I've got a sheltered cold frame so I'll put them in there. That's good because I can make good use of the freed up space on the windowsill.